(1) Field of the Invention
The present invention relates to a projector with a detachable liquid crystal panel attached thereon. More specifically, the present invention relates to a portable projector with a small detachable liquid crystal panel for displaying pictures in accordance with externally supplied video signals, and the pictures displayed on the small liquid crystal panel are magnified to form images, thereby forming an optical system.
(2) Description of the Related Art
In accordance with the progress of process technology for thin film transistors (TFT), liquid crystal panels have become finer and larger. Now, liquid crystal TVs ("LCD TVs") are available for practical use.
However, it is technically more difficult to manufacture large LCD panels than to manufacture small, fine LCD panels due to process problems. Further, the price becomes higher.
Therefore, in manufacturing an LCD TV of over 40 inches, it is advantageous to optically expand a small panel through projection. Practically, direct viewing LCD panels are used for computer monitors and portable TVs.
FIG. 1 illustrates a construction of a conventional single plate type LCD projector.
As shown in FIG. 1, the conventional single plate type LCD projector includes: an arc lamp 1, a reflector 2, an infrared ray filters 3, a first polarizing plate 4, an LCD panel 5, a second polarizing plate 6, and an image forming lens system 7.
If signals to be displayed on the LCD panel 5 are transmitted from a signal processing section (not shown) then an illuminating light almost like natural color, emitted from the arc lamp 1, is reflected back by the reflector 2 and irradiated on the LCD panel 5.
The illuminating light which is irradiated from the reflector 2 undergoes a filtering at the infrared ray filter 3 to eliminate infrared rays and ultraviolet rays which deteriorate the LCD panel. Then, the filtered light rays pass through the first polarizing plate 4 which passes only linearly polarized rays. The light rays which are thus passed are then irradiated on the LCD panel 5.
When the illuminating light rays are irradiated onto the LCD panel 5, the incident linearly polarized rays are rotatingly outputted in accordance with the pixel driving signals of the signal processing section.
The light rays which have passed through the LCD panel 5 have transmittance differences in accordance with the phase difference relative to the polarized light rays which are rotated at the LCD panel by the second polarizing plate 6. Therefore, contrasts are generated between the respective pixels. Then, the rays are magnified by the image-forming optical system 7 to form an image on a screen 8.
However, in the above described conventional LCD projector, the pictures which are projected on the screen become ambiguous in a bright environment. In other words, the picture which is projected on the screen is composed of pixels of red (R), green (G), and blue (B), and, in accordance with the brightness of the respective pixels, the gradation, i.e., contrasts are decided.
For example, if the surrounding illumination is dark, that is, if the surrounding brightness is 0; if it is assumed that the brightness of the pixels are S1=10, S2=20, S3=30, S4=40, S5=50; and if the ambient brightness is 100: the brightness of the respective pixels become S1'=110, S2'=120, S3'=130, S41=140, and S5'=150.
On the other hand, if the ambient brightness is dark, the pixels S1-S5 gain a contrast of S5:S1=5:1 at maximum. However, if the ambient brightness is bright, the contrast becomes as low as S5':S1'=1.36:1.
Accordingly, if the ambient brightness is too bright, the contrast of the picture becomes aggravated, and therefore the projected pictures are difficult to discern. Further, if the projected pictures are to be discerned, a brighter illuminating source has to be used. Consequently, the power consumption increases, and the apparatus can be damaged due to the increased heat release.